1. Field of the Invention
The present invention relates to an explosive device for transmitting an explosion from a donor detonating cord to a receiver, usually low-energy, detonating cord, and to an assembly containing said explosive device for the connection of said cords and initiation of the receiver cord.
2. Description of the Prior Art
The hazards associated with the use of electrical initiation systems for detonating explosive charges in mining operations, i.e., the hazards of premature initiation by stray or extraneous electricity from such sources as lightning, static, galvanic action, stray currents, radio transmitters, and transmission lines, are well-recognized. For this reason, non-electric initiation through the use of a suitable detonating fuse or cord has been looked upon as a widely respected alternative. A typical high-energy detonating cord has a uniform detonation velocity of about 6000 meters per second and comprises a core of 6 to 10 grams per meter of pentaerythritol tetranitrate (PETN) covered with various combinations of materials, such as textiles, waterproofing materials, plastics, etc. However, the magnitude of the noise produced when a cord having such PETN core loadings is detonated on the surface of the earth, as in trunklines, often is unacceptable in blasting operations in developed areas. Also, the brisance (shattering power) of such a cord may be sufficiently high that the detonation impulse can be transmitted laterally to an adjacent section of the cord or to a mass of explosive which, for example, the cord contacts along its length. In the latter situation, the cord cannot be used to initiate an explosive charge in a borehole at the bottom (the "bottomhole priming" technique), as is sometimes desired.
Low-energy detonating cord (LEDC) was developed to overcome the problems of noise and high brisance associated with the above-described 6-10 grams per meter cord. LEDC has an explosive core loading of only about 0.02 to 2 grams per linear meter of cord length, and often only about 0.4 gram per meter. This cord is characterized by low brisance and the production of little noise, and therefore can be used as a trunkline in cases where noise has to be kept to a minimum, and as a downline for the bottom hole priming of an explosive charge.
Until recently, most LEDC described in the art had a continuous core of a granular cap-sensitive high explosive such as PETN heavily confined in a metal sheath or one or more woven textile sheaths. An improved LEDC which is light-weight, flexible, strong, and non-conductive, detonates at high velocity, and is readily adapted to high-speed continuous manufacturing techniques is described in Belgian Pat. No. 863,290, granted July 25, 1978, the disclosure of which is incorporated herein by reference. This improved cord has a continuous solid core of a deformable bonded detonating explosive composition comprising a crystalline high explosive compound admixed with a binding agent, and a protective plastic sheath enclosing the core, no metal or woven textile layers being present around the core or sheath. Preferably, one or more continuous strands of reinforcing yarn, e.g., running substantially parallel to the core's longitudinal axis, are present outside the core. The loading of crystalline high explosive in the bonded explosive core is about from 0.1 to 2 grams per meter of length. This cord can be initiated reliably by means of a coaxially abutted blasting cap, but not by the detonation of another length of detonating cord with which it is spliced or knotted.
In the past, explosive booster charges have been employed to transmit a detonation impulse from a main line of LEDC to a branch line of detonating fuse. U.S. Pat. No. 3,205,818, for example, shows a booster charge of a high-velocity detonating explosive contained in a capsule which is crimped to one end of a length of LEDC which abuts the booster charge. The bottom, closed end of the capsule is positioned adjacent to the side of a length of detonating fuse. The booster charge is used when the detonation impulse is to be transmitted from the LEDC to the detonating fuse. This booster-connector has to be pre-assembled with the LEDC at the place of manufacture to seal the capsule, thereby protecting the booster charge until the time of use. As a result, the booster-connector can be used only with a fixed length of LEDC. Furthermore, the booster charge described in U.S. Pat. No. 3,205,818 is stated therein to be useful with a type of LEDC that requires the booster to transmit a detonation impulse from itself to detonating fuse, but not in the reverse direction.
A booster which does not depend on its pre-assembly with a detonating cord for sealing, but rather is a self-contained, sealed unit adapted to receive and hold a detonating cord in position, the booster and cord being assembled usually at the time of use, would offer such advantages as safety and convenience because of the separated conditions of the components of the assembly during handling and storage, possible separate classification of the components for transportation, etc. In addition, a booster which would function reliably with less-sensitive low-energy detonating cords, i.e., those of the type which require a booster to be initiated by, as well as to initiate, detonating fuse, would offer the advantage of being applicable to more types of cords, including the type described in the aforementioned Belgian patent.